Method and composition for a furan-modified phenolic novolak binder system

ABSTRACT

A method and composition for forming a dry free-flowing particulate solid is disclosed which utilizes a novel binder system for bonding particles of carbon, sand and/or other solid particulate materials. The solid, non-sticky binder system comprises furfural, solid resin, (such as a phenolic resin), which is not sticky at room temperature and is soluble in furfural, and a liquid amine having free hydrogens on the amine nitrogen which amine is capable of reacting with furfural. This system is capable of adhering to such particles while retaining the free-flowing characteristics of the particles. The free-flowing particulate solid thus formed may be shaped, extruded or compression molded as necessary to form the desired article. A shaped mass of this particulate material is converted to an integral mass by warming or compressing. While the binder is curable at room temperature over a long period of time, the cure rate may be accelerated by increases in temperature. Carbonization of the resin system yields a high carbon residue.

BACKGROUND OF THE INVENTION

This application relates in general to a method for forming a resinbinder system and more preferably to a method for forming a resin bindersystem of a furfural-phenolic resin system.

Furan modified phenolics have found great favor recently, largelybecause of their capability of providing high carbon content, highstrength and thermosetting characteristics. However, because of theliquid nature of such furan phenolics, difficulties in their use werepresented. For example, mixing with sand to form a foundry shapeproduced a heavy, sticky or viscous mix which was hard to work with.Mixing with carbon for subsequent molding or extrusion produced a stickymix with little green strength.

Attempts to solve the above problem to render furan modified phenolicsmore acceptable for use with refractory materials in forming desiredshapes and articles, as typified by U.S. Pat. No. 4,051,301 to Laitar,have resulted in a solid thermoplastic resin which, when added to arefractory material such as sand, had to be heated or otherwisedissolved to result in a free-flowing particulate mix that can beconverted to a hard rigid thermoset article. However, this desirable endresult is achievable only through the use of an expensive formulationprocedure, thereby putting the resin in an unfavorable economic positionwith traditional phenolic novolaks.

SUMMARY OF THE INVENTION

An object of the present invention is a free-flowing non-stickyparticulate mixture of a high furfural content binder and a solidparticulate material.

An additional object of this present invention is an economicalfree-flowing particulate mixture having a binder of a furan-modifiedphenolic.

An object of the subject invention is a furan-modified phenolic binderwhich has a long storage life.

Another additional object of the present invention is a solid non-stickythermoplastic furan-modified phenolic binder which can be handled andprocessed at room temperatures and yet is thermosetting at moderatetemperatures.

A still further object of the present invention is a catalyzed, longbench life coated particulate mixture capable of being converted to anintegral mass by warming or pressure.

These and other objects of the present invention are provided by themethod and composition for forming a free-flowing stable particulate mixhaving a binder of a high furfural content system, such as, for example,a furfural-phenolic resin system. A preferred binder system is generallyformed by admixing a liquid blend of a solid non-sticky novolak resinand furfural to a particulate material having a small amount of theliquid amine uniformly dispersed thereon. Mixing is continued until theentire mass breaks into a free-flowing particulate mixture. Theresulting particulate material may be shaped, extruded, or compressionmolded, depending upon the desired end product, and is converted to anintegral mass by warmth or compression.

Consider broadly, the objects of this invention are achieved bydissolving a solid non-sticky resin in furfural monomer in an amountsufficient to reduce the viscosity of the solution to a level at whichthe solution can be uniformly admixed with a particulate solid materialsuch as carbon, sand, glass fibers, other refractory materials, and thelike. Upon addition of the resulting solution to particulate materialcontaining the amine the resulting mass is transformed to a "dry" (i.e.no liquid) free-flowng particulate mass. The amines which are used areof the class which are liquid at ambient room temperatures, and capableof forming a reaction product with furfural.

DETAILED DESCRIPTION OF THE INVENTION

In a preferred embodiment of the subject invention a phenolic novolakresin is mixed with furfural so as to achieve a desired viscosity aswill be discussed. Generally speaking, as used herein, the term"novolak" and "novolak resin" denote a condensation product such as isobtained by causing a phenol to condense with less than an equimolarportion of an aldehyde or a ketone, in an acidic environment.Structurally the molecules of a novolak consist essentially ofalkyl-substituted or unsubstituted phenyl nuclei connected together bymethylene or substituted methylene links.

To form a preferred novolak suitable for use in the subject invention amixture of phenol and aqueous formaldehyde is prepared at a ratio of1.15 moles phenol to 1.00 moles of formaldehyde. A sufficient quantityof oxalic acid is admixed therewith to provide a pH of about 1.0 and thereaction mixture is allowed to react under atmospheric refluxtemperature conditions until all of the formaldehyde disappears.Thereafter, a sufficient quantity of aqueous sodium hydroxide is addedto the reaction mixture to elevate the pH of the reaction mixture toapproximately 6.3. Thereafter the refluxing condensor is removed andmost of the water and unreacted phenol is allowed to be removed from thereaction mixture in the conventional reduced pressure distillationstripping step. The resulting resin is a solid at room temperature.While reference is made herein to a specific manner of preparing a solidnovolak, other methods as are known and accepted in the art may beutilized.

To the novolak prepared as indicated above, furfural is added insufficient quantities to achieve a desired viscosity. The furfural maybe either added to the novolak while still in melted condition in thenovolak reactor or solid novolak may be added to the furfural. Thefollowing table indicates approximate amounts of furfural as percentagesof the whole mixture which may be added to the novolak to obtain a givenviscosity.

                  TABLE I                                                         ______________________________________                                        % Furfural    Viscosity (cps)                                                 ______________________________________                                        44%           3000                                                            48%           900                                                             53%           400                                                             57%           250                                                             69%           180                                                             74%            65                                                             ______________________________________                                    

The furfural-novolak solution thus prepared has a long shelf life atroom temperature and, though liquid and completely adjustable inviscosity, is completely reactive, all components becoming a part of thesolids of the cured resin. However, inclusion of the reactive amine withthis solution, in accordance with the present invention, converts it toan uncured but solid, non-sticky condition. The resulting solid isthermoplastic. However, because the amine can convert the system into athermoset condition, the amine-containing admixture is a catalyzedbinder system when dispersed on a particulate solid in accordance withthe present invention.

Although the particulate solids coated in accordance with this inventioncontain the amines, they are essentially uncured and are capable ofbecoming plastic or semi-liquid on heating. This allows the particulatesolids to be molded or extruded. When furfural is added to the novolakin an amount more than double that of the novolak by weight the excesswould appear to be wasteful. The minimum amount of furfural to be addedto the novolak is that which is sufficient to liquify the novolak.Furfural to novolak ratios of 0.6:1.0 to 2.0:1.0 are preferred.

Preferably the amines of the subject invention are liquid mono- orpoly-amines having two or more free hydrogens on the amine nitrogen anda boiling point over 150° C. However lower boiling amines such asammonia or ethylene diamine may be used. The most preferred amine istriethylenetetramine (TETA).

As a result of the six free hydrogens available in TETA for reactionwith furfural molecules, a relatively small amount of TETA will bind upat room temperature the liquid furfural in the furfural novolak mixture,transforming such a mixture into the thermoplastic solid. Thus when theTETA is initially dispersed on an aggregate such as sand or carbon, andthe furfural-novolak resin blend added, the resin system essentiallycoats the sand or carbon particles, as will be discussed in greaterdetail hereinafter, with no free furfural, as evidenced by the absenceof the pungent furfural odor. The result is a dry free-flowingparticulate solid which has good bench life, and, while beingthermoplastic, can be completely thermoset by baking at moderatetemperatures. Alternatively the binder system can be cured at roomtemperature over a long period of time. The curing rate of the resinbinder system can be adjusted by increasing or decreasing the amount ofthe amine. For instance the amount of 4 percent TETA based on thefurfural present will provide greater shelf life at room temperature,while increasing the amount of TETA up to a maximum of 30 percent willincrease the curing rate. The minimum amount of amine which can be usedin accordance with this invention is the amount which will react withthe furfural in the novolak-furfural solution to convert it at roomtemperature to an uncured solid. Mixing of the amine with the furfuralresin solution is carried out at room temperature with cooling if themixing conditions require cooling. Preferably the amine is added to thesolid particulate substrate prior to addition of the furfural resinsolution.

As stated above, the resin binder system of the subject invention isuseful in forming articles and shapes from a wide variety of particulatesolid material. The following examples illustrate some of those uses andare not to be taken as limiting in any respect. All parts andpercentages, unless expressly stated to be otherwise, are by weight.

EXAMPLE I

Approximately 2 percent of triethylenetetramine (TETA) and 70-75 percentcarbon particles are thoroughly blended. To this dry amine-carbonmixture is added 16-23 percent of a liquid mixture of thefurfural-novolak resin, prepared as described above to have a viscosityof 2500 cps. The mixing apparatus was cooled throughout the blending ofthe ingredients. Within 10 minutes of the addition of the resin bindersystem, the temperature of the resulting mixture started droppinggradually from a peak of 50°-60° C. Mixing of the ingredients wascontinued for a total of twenty minutes when a dry, free-flowingparticulate solid was obtained. No furfural fumes were observed to beemitted during the mixing procedure.

The free-flowing powder was later placed into a preheated (60°-65° C.)extruder and extruded through a die into rods. The resulting rods, uponbeing cooled to room temperature, were found to be very hard and solid,with good green strength. The green carbon rods were baked andthoroughly carbonized by baking in a reducing atmosphere with aprogrammed temperature rise to 650° C. and holding at that temperaturefor 48 hours. When carbonized, the rods had satisfactory density andresistivity for use as electrodes. No bleeding or cracking was observed.The stack gases from the carbonization furnace were reduced inobjectionable gases.

In practice the carbon particle portion of the mix may be formed from avariety of carbon sources, the percentages of which may vary, accordingto availability and other considerations. An actual formulation maycontain carbon in the form of baked scrap, i.e. that scrap already bakedand subsequently rejected for reasons such as quality control, and greenscrap or that scrap which has been extruded yet not baked. A petroleumproduct such as a high viscosity (1500 cps) oil, may also be added forlubrication purposes. The following formulations are set forth to showthe range of ingredient compositions yielding satisfactory carbon rods.

                  TABLE II                                                        ______________________________________                                                     Formulation No.                                                  Ingredients    I       II      III   IV   V                                   ______________________________________                                        Coarse Calcined                                                               Petroleum Coke 44.8%   38.5%   40.1% 43%  36%                                 Baked Scrap    29.8    26.0    26.6  20.0 32                                  Green Scrap     --     13.0    13.3  10.0 12.0                                Oil (1500 cps)  0.9     0.8     0.9   2.8  2.8                                Furfural-Phenolic Resin                                                       System (2500 cps)                                                                            23.3    20.3    17.8  22.0 15.7                                TETA            1.2     1.0     1.3   2.2  1.5                                ______________________________________                                    

EXAMPLE II

92.3 parts coke particles of one-quarter inch mesh or smaller were mixedwith 0.7 parts TETA and 7 parts of the furfural phenolic resin blend(3000 cps) was added; the mixing action was continued for twenty minuteswith cooling until a free-flowing granulated solid resulted. Thefree-flowing solid was compression molded into five inch cubes useful asa source of carbon when added to molten iron as a cupola meltingredient.

EXAMPLE III

83.8 parts silicon carbide aggregate were mixed with 1.2 parts TETA.Fifteen parts of the furfural phenolic resin blend (3000 cps) was addedto the dry silicon carbide and TETA; the mixing action was continuedwith cooling until a free-flowing granulated solid was attained. Thegranulated solid was formed into a crucible one foot in diameter by twofeet in depth through a shaping mold having a conventional rotatingscribe. The resulting green crucible shape was separated from the moldand cured at 65° C. for 24 hours. The cured crucible was then carbonizedat 800° C. under a reducing atmosphere.

EXAMPLE IV

91.7 parts grated aggregate of calcined dead-burned magnesite having aparticle size of no greater than one-quarter inch mesh and 3 parts finecarbon powder was blended with 0.3 parts TETA. Five parts of thefurfural phenolic resin mixture (3000 cps) described above was added tothe magnesite, carbon and TETA; mixing was continued until a dryfree-flowing granulated solid results. The granulated solid wascompression molded in the shape of a large brick at 145° C. A highertemperature is required to cure refractory bricks in this applicationbecause of the large size of the brick and its poor heat conductivity.Alternatively the brick may be cold-molded and then baked at 95° C. for24 hours. The resulting refractory brick may be used to form furnacelinings and the like.

EXAMPLE V

93.5 parts foundry sand, Wedron 5025, was mixed with 0.3 parts TETA. 3.5parts of the furfural phenolic resin mixture (3000 cps) described abovewas added to the sand-TETA blend and mixed until a dry free-flowingsolid resulted. A surplus quantity of the above mix is placed against amold pattern heated to 175° C. for a sufficient time to produce a shellmold of desired thickness, for instance, 60 seconds. The mold wasinverted and the surplus mix dropped into a conventional recovery sandunit. The resulting formed sand mold was removed from the pattern.

EXAMPLE VI

89 parts granulated carbon was blended with 1.0 partshexamethylenetetramine. 10 parts of the furfural-phenolic resin (3000cps) described previously was added and mixing was continued. A sticky,viscous lumpy mix resulted having a furfural odor. The sticky mix wasincapable of being easily molded or handled.

EXAMPLE VII

89 parts granulated carbon was blended with 10 parts triethanolamine. 10parts of the furfural-phenolic resin (3000 cps) described above wasadded and mixing continued. A sticky viscous lumpy mix having thedistinct odor of furfural resulted. The sticky mix could not be easilymolded or handled.

A review of the above examples will show that the use of the liquidaliphatic amine TETA, which has free hydrogens available for interactionwith the furfural molecule, was capable of providing dry free-flowingmixtures with the furfural phenolic resins. The failure of bothtriethanolamine and hexamethylenetetramine to provide a dry free-flowingmix can be explained by their lack of free hydrogens on the aminelinkages. The aliphatic structure of TETA and other similar aminesprovides the necessary free hydrogens for tying up the furfuralmolecules, resulting in the solid free-flowing mixture observed.

While applicants herein do not wish to be bound by any theory, it isbelieved that the individual aggregate particles of the particularrefractory material used are coated with the furfural-phenolic-TETAresin complex. This solid uncured resin complex, though adhering to therefractory particle, does not cause the coated particles to adhere toeach other, thus creating the free-flowing dry powder observed. Whenadvanced to the cured state, for example by a long period of time atroom temperature or by low temperatures such as 60° C. Upon heating, thecoating on the individual particles becomes initially liquid as inthermoplastic resins, whereby the mass exhibits good molding andextrusion characteristics, the resulting shaped mass exhibiting goodgreen strength, and finally setting to a hard, thermo-set rigid shape.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

We claim:
 1. A method for forming shapes comprising the steps ofa. mixing particles of a solid particulate material and a liquid amine capable of reacting with furfural into a substantially uniform blend; b. mixing at room temperature said blend from step (a) with a resin system comprising a phenolic novolak resin dissolved in furfural; c. continuing mixing until a free-flowing dry particulate solid results, and d. forming said particulate solid into a desired shape whereby shapes of refractory material with satisfactory green strength are formed, said shapes being capable of being baked and carbonized.
 2. The method of claim 1 wherein said liquid amine is a liquid aliphatic amine having free hydrogens on the amine nitrogen and a boiling point of 150° C.
 3. The method of claim 1 wherein said liquid amine is triethylenetetramine.
 4. The method of claim 1 wherein said solid particulate material is carbon.
 5. The method of claim 4 wherein said free-flowing particulate solid is extruded into a carbon rod.
 6. The method of claim 4 wherein said free-flowing particulate solid is compression molded into blocks for use as a cupola melt ingredient.
 7. The method of claim 1 wherein said solid particulate material is silicon carbide.
 8. The method of claim 7 wherein said free-flowing particulate solid is formed into a crucible shape in a shaping mold and thereafter baked and carbonized.
 9. The method of claim 1 wherein said solid particulate material includes calcined dead-burned basic refractory material.
 10. The method of claim 9 wherein said solid particulate material is compression molded under heat to form a refractory brick.
 11. The method of claim 1 wherein said solid particulate material includes sand.
 12. The method of claim 11 wherein a surplus quantity of said free-flowing particulate solid is placed against a heated mold pattern for a sufficient time to produce a shell mold of desired thickness.
 13. A method for forming carbon rods by extrusion, comprising the steps ofa. mixing carbon particles and a liquid amine capable of reacting with furfural into a substantially uniform blend; b. mixing a phenolic novolak dissolved in furfural with said blend until a free-flowing dry solid results; c. placing said dry solid into an extruder; d. extruding said dry solid to form carbon rods of good green strength; e. cutting said green carbon rods, and f. baking and carbonizing said carbon rods under a reducing atmosphere.
 14. The method of claim 13 wherein said amine is triethylenetetramine.
 15. The method of claim 13 wherein said baking and carbonizing includes the steps of placing said green carbon rods into a furnace and raising the temperature of said furnace in a programmed manner to 650° C. under a reducing atmosphere and holding at that temperature.
 16. A method of manufacturing a composition consisting of free-flowing non-sticky particulate solids capable of being shaped and integrated into a unitary mass, said method comprising steps ofa. preparing a furfural solution of a phenolic novolak said furfural being present in an amount sufficient to provide a viscosity of the resulting solution sufficiently low to uniformly distribute the solution on particulate solid material; and b. admixing the resulting solution with a mixture of particulate solid material and an amine, said amine being capable of reacting with furfural to produce a solid, said amine having free hydrogens on the amine nitrogen;said amine being used in an amount sufficient to convert the furfural resin solution into an uncured solid, said mixing taking place at temperatures not exceeding 50° C., continuing the mixing until a free-flowing dry particulate solid results.
 17. The method of claim 16 wherein the amine is triethylenetetramine.
 18. The method of claim 16 wherein the particulate solid material comprises carbon.
 19. The method of claim 16 wherein the particulate material includes sand.
 20. The method of claim 16 in which the particulate material includes calcined dead-burned basic refractory material. 